1. Field of the Invention
The invention is directed to an improved flap valve for controlling a gas flow and more particularly to such a valve especially useful in controlling the flow in a gas flow system of an internal combustion engine.
2. Description of the Prior Art
In a known throttle valve for controlling a gas flow in an exhaust conduit of an internal combustion engine, disclosed in DE 43 05 123 A1, the flap shaft which supports the throttle valve and extends parallel to the flap surface of the throttle valve is supported at both ends by a bearing bore in the conduit wall of the exhaust conduit and respectively protrudes through a bearing sleeve there. In order to achieve a greater degree of tightness while avoiding a sluggishness of the flap actuation, the bearing sleeves, which are each axially prestressed by means of spring force in a respective bearing housing, can move in a radial direction inside the bearing housing, as a result of which the dimensional deviations between stop surfaces for the throttle valve, which are embodied on the conduit wall, and the flap shaft bearing are automatically compensated for when the throttle valve first closes.
The unpublished patent application DE 199 34 113.3 has already disclosed using a flap valve of the type mentioned at the beginning as an exhaust return valve for the metered admixing of exhaust into the aspirated fresh air in the intake section of an internal combustion engine. To this end, the casing of an intake tube of the intake section is provided with an opening into which the valve outlet of the flap valve is inserted in a gas-tight manner. With a flap shaft that is inclined in relation to the flap plane for flap adjustment, the valve flap is disposed in a thin-walled tube, which is inserted into the rigid valve tube with radial play and is fastened to the valve tube with a tube section. Through an appropriate shaping of the valve flap, in its closed position, the valve flap conforms to the inner wall of the elastic thin-walled tube and closes the tube cross section in a gas-tight manner so that a separate seal between the valve tube and the valve flap can be eliminated.